Anion-exchange Step Research Articles

Langmuir-Hinshelwood-Hougen-Watson Heterogeneous Kinetics Model for the Description of Fe (II) Ion Exchange on Na-X Zeolite

This study aimed to investigate the kinetics of the anion exchange step of ferrous ions with Na-X zeolite in a temperature range of 20 and 80°C for a period of up to 8 hours. A ferrous sulfate heptahydrate solution was used as a ferrous ion source to exchange with the sodium of the Na-X zeolite. The results showed a change in the physical appearance of the zeolite with the progress of the ion exchange process. The catalyst color was observed with the progress of the ion exchange time and changed from yellow to brown. The ferrous ion exchanged contents increased with temperature and reached 0.519 at 80°C after 8 hours. A kinetic model based on the Langmuir-Hinshelwood-Hougen-Watson model was suggested and developed to describe the ion-exchange process. The proposed model was solved numerically, and the results indicated its ability to describe the experimental results with high correlation coefficients. Finally, the activation energy for the forward reaction was 31590.7J/mole compared to 28105.5J/mole for the backward, and the frequency factors for the forward and backward reactions were investigated.

Heteroepitaxial growth of core-shell ZnO/CdS heterostructure for efficient and stable photocatalytic hydrogen generation

Solar-driven water splitting provides a promising way to generate clean and renewable hydrogen. The efficiency and stability are of importance for practical application of this technology. Herein, colloidal ZnO/CdS heterostructure catalysts were obtained via a two-step heteroepitaxial growth strategy. It was discovered that the anion exchange step plays an important role in construction of core-shell ZnO/CdS heterostructure and photo-induced electron-hole separation is promoted by reducing the charge carriers transfer distance in prepared ultra-small heterostructure. By optimizing the molar ratio of the ZnO and CdS components, the highest hydrogen generation rate of 669.6 μmol/h (100 mg) was achieved without any cocatalyst loading in the presence of S2− and SO32− as sacrificial reagents. Furthermore, the heterostructure displayed excellent photocatalytic stability for ∼72 h. The photocatalytic performance of as-prepared nanoscale ZnO/CdS is superior than that of the well-studied bulk ZnO/CdS heterostructures, demonstrating its great potential in practical application of photocatalytic water splitting.

Recovery of high specific activity molybdenum-99 from accelerator-induced fission on low-enriched uranium for technetium-99m generators

A new process was developed to recover high specific activity (no carrier added) 99Mo from electron-accelerator irradiated U3O8 or uranyl sulfate targets. The process leverages a novel solvent extraction scheme to recover Mo using di(2-ethylhexyl) phosphoric acid following uranium and transuranics removal with tri-n-butyl phosphate. An anion-exchange concentration column step provides a final purification, generating pure 99Mo intended for making 99Mo/99mTc generators. The process was demonstrated with irradiated uranium targets resulting in more than 95% 99Mo recovery and without presence of fission products or actinides in the product.

Comparative evaluation of integrated purification pathways for bacterial modular polyomavirus major capsid protein VP1 to produce virus-like particles using high throughput process technologies

Modular virus-like particles and capsomeres are potential vaccine candidates that can induce strong immune responses. There are many described protocols for the purification of microbially-produced viral protein in the literature, however, they suffer from inherent limitations in efficiency, scalability and overall process costs. In this study, we investigated alternative purification pathways to identify and optimise a suitable purification pathway to overcome some of the current challenges. Among the methods, the optimised purification strategy consists of an anion exchange step in flow through mode followed by a multi modal cation exchange step in bind and elute mode. This approach allows an integrated process without any buffer adjustment between the purification steps. The major contaminants like host cell proteins, DNA and aggregates can be efficiently removed by the optimised strategy, without the need for a size exclusion polishing chromatography step, which otherwise could complicate the process scalability and increase overall cost. High throughput process technology studies were conducted to optimise binding and elution conditions for multi modal cation exchanger, Capto™ MMC and strong anion exchanger Capto™ Q. A dynamic binding capacity of 14 mg ml−1 was achieved for Capto™ MMC resin. Samples derived from each purification process were thoroughly characterized by RP-HPLC, SEC-HPLC, SDS-PAGE and LC-ESI-MS/MS Mass Spectrometry analytical methods. Modular polyomavirus major capsid protein could be purified within hours using the optimised process achieving purities above 87% and above 96% with inclusion of an initial precipitation step. Purified capsid protein could be easily assembled in-vitro into well-defined virus-like particles by lowering pH with addition of calcium chloride to the eluate. High throughout studies allowed the screening of a vast design space within weeks, rather than months, and unveiled complicated binding behaviour for CaptoTM MMC.

Selenium oxyanion exchange with Mg(II)-Fe(III) and Fe(II)-Fe(III) layered double hydroxides

Immobilization of selenium oxyanions from water resources is a helpful strategy to mitigate exposure to Se at concentrations toxic to human and ecosystem health. Pyroaurite-type minerals are layered double hydroxides with high anion exchange capacity with relevance in subsurface environments and applicable to water treatment technologies. Three types of Mg(II)-Fe(III) pyroaurites and Fe(II)-Fe(III) green rusts were evaluated in kinetic studies to determine the influence of different interlayer anions on the uptake of dissolved selenate (SeO42−) and selenite (HSeO3−, SeO32−). Selenate and selenite uptake extents with pyroaurites were controlled by the identity of the interlayer anion according to the order Cl−> SO42−> CO32−, as predicted by known interlayer anion preferences for LDH. The kinetics of Se uptake typically expressed a rapid initial anion exchange step followed by a slow re-exchange back to solution due to competition with expelled interlayer anions. Excess dissolved interlayer anions and high pH values exacerbated this reverse exchange of Se. The results suggest Se oxyanions taken up by pyroaurites may not be firmly sequestered. Selenate uptake by redox-active green rust appears to be subject to the same interlayer anion preference as non-redox active pyroaurite, suggesting that the ability of green rust to reduce selenium oxyanions may be limited by the anion exchange process.

Automated pH and conductivity conditioning using feedback control to support a two-step continuous purification process

As discovery research organizations push more molecules and new modalities through their company pipelines, there comes a need to widen purification development and production bandwidth by increasing automation and throughput. Continuous processing technologies have the unique property of reducing manufacturing floor space and reducing costs. We can speed development and production by implementing automation and continuous process technologies early in discovery research. Here we describe an automated continuous instrument made up of an ÄKTA™ pcc for initial capture by protein A, an ÄKTA pure 150 retrofitted to automatically condition protein A eluate, and a second ÄKTA pure 150 built for flow-through anion exchange chromatography. The continuous instrument we have designed and built recirculates protein A eluate from the ÄKTA pcc in a closed loop while signals from the pH and conductivity meters direct addition of titrant for accurate and precise adjustments to the pH and salt concentration. The instrument is run without user intervention and can be used continuously for production or for development as a tool for screening running conditions on the anion exchange step.

Aconitic acid recovery from sugar-cane stillage: From the modeling of the anion-exchange step to the conception of a novel combined process

ABSTRACT Sugarcane stillage is rich in tri-carboxylic aconitic acid. To study its purification through anion-exchange, selectivity coefficients between aconitate and the major competing minerals were determined on a weak-base resin for different pH. Simulation of solutes separation in the column, using mass conservation equations and equilibrium theory, confirmed that resin in sulfate form and pH = 4.5 led to the best separation performances, and showed that a preliminary chloride removal up to 0.5 g L−1 was the most profitable to increase the ionic exchange capacity for aconitic acid. Demineralization of a real stillage by conventional electrodialysis followed by the optimized ion-exchange step led to an aconitic acid-rich extract.

Separation method for Pu, Am and Sr in large air filter sample sets

A sequential separation method for Pu, Am, and Sr was applied for unusually large sample sets of air filters. The sample sets were combined weekly air filters covering sampling time from three months to five years, while in original method, the analyzed air filters had sampling time of only 1-3 days, containing significantly less organic and inorganic matrix and natural radionuclides. The separation method is based on ashing and wet-ashing, followed by column separations with extraction chromatography and anion exchange. Reference materials IAEA-447, IAEA-384, and NIST-SRM-4353A were analyzed with the modified separation method. IAEA-384 was representing best the composition and radionuclide level in the air filter samples.•Compared to the original method, sample ashing took considerably longer time (one day vs. several days).•High concentration of natural radionuclides in the large air filter sample sets interfered first the determination of 241Am and 90Sr, until an anion exchange step was adopted for removal of 210Bi and 210Po from Am and Sr fractions.•After modification, the method is suitable for separating artificial radionuclides 238,239,240Pu, 241Am, and 90Sr from large sample sets of air filters.

One-pot Synthesis of Unsymmetrical Diaryliodonium Tetrafluoroborate Salts Bearing an Isoxazole Moiety from Aryl Boronic Acids

Hypervalent iodine compounds exhibit attractive features of low cost, mild and selective reagents in organic synthesis. These reagents serve as environmentally benign alternatives to toxic heavy-metal based oxidants and expensive organometallic catalysts. The practical and simple synthesis of unsymmetrical diaryl iodonium tetrafluoroborate salts is described. This synthetic method has allowed the production of isoxazole tetrafluoroborate salts from readily available aryl boronic acids without an extra anion exchange step in acceptable yields of 45% and 50%.

Ultrafine Co2P anchored on porous CoWO4 nanofiber matrix for hydrogen evolution: Anion-induced compositional/morphological transformation and interfacial electron transfer

Even though transition metal phosphides (TMPs) have been regarded as very promising catalysts for hydrogen evolution reaction (HER), exploring highly reactive TMPs-based catalysts with reliable stability in alkaline media remains an enormous challenge. Herein, using wafer-like Co(CO3)0.5(OH)·0.11H2O as template followed by anion-exchange and further phosphorization process, it is synthesized a three-dimensional (3D) hierarchical porous heterostructure with highly dispersed ultrafine metallic Co2P nanoparticles uniformly anchored on porous conductive CoWO4 nanofiber matrix, which not only promotes the electron transfer, but also avoids the deterioration of phosphide. In addition, the electron densities re-distribution within the heterostructure also contributes to the improved catalytic activity. Furthermore, the doping of W into Co2P gives proper H adsorption free energy ΔGH. Impressively, the Co2P/CoWO4/Ni foam (NF) exhibits an overpotential of 81 mV at −10 mA cm−2 and a Tafel slop of 47 mV dec−1 along with supreme long-term durability at −40 mA cm−2. The present work also demonstrates different dosages of Na2WO4 in the anion-exchange step will lead to different phase compositions and morphologies, giving rise to different HER electrocatalytic performances of the phosphorized samples.

One step Purification and Characterisation of Abrin Toxin from Abrus Precatorius Seeds

Abrin is a plant toxin obtained from Abrus precatorius seeds. It belongs to the type II ribosomal inactivating proteins (RIPs) consisting of two chains namely, catalytically active A chain and sugar binding B chain linked by a single disulphide bond. Due to high toxicity of abrin, its exposure or consumption can lead to serious public health problems. In the present work, we have extracted and purified the abrin toxin from Abrus precatorius seeds. The toxin was purified using a single step anion exchange chromatography. The purified protein was characterized by SDS-PAGE and MALDI- TOF to confirm its purity. The toxicity of purified abrin toxin was also confirmed by injecting the toxin in mice. The purified protein was further used to raise antibodies in mice and characterized by indirect Enzyme Linked Immunosorbent Assay. The results of present study established the use of single step ion exchange chromatography to purify abrin toxin for further development of its detection system.

Development of ZIF-Derived Nanoporous Carbon and Cobalt Sulfide-Based Electrode Material for Supercapacitor.

Zeolitic Imidazolate Framework (ZIF-67) was prepared in two different solvents—water and methanol. Nanoporous carbon was derived from ZIF-67 via pyrolysis in an inert atmosphere. Anion exchange step of sulfidation on the synthesized material has a great influence on the structure and properties. Structural morphology and thermal stability were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM)/energy dispersive x-ray spectroscopy (EDS), Brunauer-Emmett-Teller (BET), and thermogravimetric (TG) analysis. The electrochemical analysis was evaluated by cyclic voltammetry, chronopotentiometry, and impedance analysis. The as-prepared nanoporous carbon and cobalt sulfide (NPC/CS) electrode material (water) in 2M KOH electrolyte solution exhibit high specific capacitance of 677 F/g. The excellent electrochemical performance of the NPC/CS was attributed to its hierarchical structure. This functionalized ZIF driven strategy paves the way to the preparation of various metal oxide and metal sulfide-based nanoheterostructures by varying the type of metal.

Exploring the separation power of mixed-modal resins for purification of recombinant osteopontin from clarified Escherichia coli lysates.

Osteopontin (OPN) is a structural protein with potential value in therapeutic and diagnostic applications. Low titer, acidic isoelectric point, and the lack of well-defined secondary and tertiary structure were some of the challenges that complicated purification development of OPN from recombinant Escherichia coli lysates. Reported processes for OPN recovery from recombinant sources use nonorthogonal unit operations and often suffer from low yield. In this work, we expanded the search for an optimal OPN purification method by including mixed-modal resins with both ionic and hydrophobic properties (Capto adhere, HEA HyperCel, and PPA HyperCel). Plate-based high-throughput screening (HTS) platform revealed useful information about the interactions between the three different ligands and OPN as function of pH and ionic strength. The HTS data allowed the selection of OPN adsorption and elution conditions that were tested and optimized in a batch mode. In terms of purification factor and yield, HEA HyperCel performed significantly better than the other two mixed-modal resins. Pairing HEA HyperCel with a strong anion exchange step (Capto Q) resulted in a two-step purification process that achieved 45-fold purification of OPN with a final purity of 95% and 44% overall yield. The orthogonality provided by mixed-modal and ion exchange steps resulted in higher yield in fewer unit operations than reported processes. © 2018 American Institute of Chemical Engineers Biotechnol. Prog., 35: e2722, 2019.

Human αB-crystallin as fusion protein and molecular chaperone increases the expression and folding efficiency of recombinant insulin.

Low expression and instability are significant challenges in the recombinant production of therapeutic peptides. The current study introduces a novel expression and purification system for human insulin production using the molecular chaperone αB-crystallin (αB-Cry) as a fusion partner protein. Insulin is composed of A- and B-chain containing three disulfide bonds (one intarchain and two interchains). We have constructed two plasmids harboring the A- or B-chain of insulin joined with human αB-Cry. This system is suitable for cloning of the genes and for directing the synthesis of large amounts of the fusion proteins αB-Cry/A-chain (αB-AC) and αB-Cry/B-chain (αB-BC). The construction of vectors, their efficient expression in Escherichia coli and simple purification of the fusion proteins and two insulin chains are described. A large amount of the recombinant fusion proteins with high purity was obtained by applying a single step anion exchange chromatography or metal chelate affinity. The insulin A- and B-chain were released from the fusion proteins using cyanogen bromide cleavage. The insulin peptides were obtained with an appreciable yield and high purity using one-step gel filtration chromatography. To increase efficiency of chain combination to produce insulin, αB-Cry was used under oxidative conditions. The purification of natively folded insulin was performed by phenyl sepharose hydrophobic interaction chromatography. Finally, using an insulin tolerance test in mice and various biophysical methods, the structure and function of purified human recombinant insulin was compared with authentic insulin, to verify folding of insulin to its native state. Overall, the novel expression system using αB-Cry is highly demanding for producing human insulin and functional protein. The procedure for αB-Cry-mediated insulin folding could be also applicable for the large-scale production of this highly important therapeutic peptide hormone.

Proceedings of the 2017 Viral Clearance Symposium, Session 2.2: DSP Unit Operations–Purification Unit Operations

The process capability and potential for various forms of chromatography to remove viruses have been discussed extensively in the literature, including the observed variability in performance of some unit operations such as Protein A and cation exchange (CEX). Some unit operations such as anion exchange (AEX) have shown robustness over a wide range of operating conditions. The robustness and effectiveness of the AEX step combined with a detailed understanding of the mechanisms that result in virus and impurity partitioning versus protein partitioning (e.g. conductivity, loading, pH range) support the feasibility of a generic or modular claim for AEX. A more fundamental understanding of the mechanisms for other chromatographic media (Protein A, CEX, and mixed-mode) could lead to more effective and more robust log reduction value (LRV) claims for these steps as well. Specific examples of CEX and mixed-mode chromatography were explored in the session and were also discussed in detail at the 2013 and 2015 Viral Clearance Symposia. Although some gaps remain in the mechanistic understanding of these unit operations, significant progress has been made and was reported at the 2017 Viral Clearance Symposium. It is important to note that recent publications on the mechanisms of viral clearance for mixed-mode chromatography and a framework for measurement of relative hydrophobicity have provided insights and new tools to better define the operating space and critical process parameters. The session also explored the use of next-generation mixed-mode adsorbers and the potential mechanisms contributing to the observed viral clearance. Gaps were also identified (e.g. integrity test when size-based mechanisms are used) and should be addressed to ensure robust viral clearance for these integrated and productive emerging unit operations.LAY ABSTRACT: Preparative chromatography is the most widely used unit operation for purification of therapeutic proteins. This session focused on the potential for various forms of chromatography to remove viruses. To advance to the next level of process, understanding the virus removal mechanism of different types of chromatography was addressed.

Secretory immunoglobulin purification from whey by chromatographic techniques.

Secretory immunoglobulins (SIg) are a major fraction of the mucosal immune system and represent potential drug candidates. So far, platform technologies for their purification do not exist. SIg from animal whey was used as a model to develop a simple, efficient and potentially generic chromatographic purification process. Several chromatographic stationary phases were tested. A combination of two anion-exchange steps resulted in the highest purity. The key step was the use of a small-porous anion exchanger operated in flow-through mode. Diffusion of SIg into the resin particles was significantly hindered, while the main impurities, IgG and serum albumin, were bound. In this step, initial purity was increased from 66% to 89% with a step yield of 88%. In a second anion-exchange step using giga-porous material, SIg was captured and purified by step or linear gradient elution to obtain fractions with purities >95%. For the step gradient elution step yield of highly pure SIg was 54%. Elution of SIgA and SIgM with a linear gradient resulted in a step yield of 56% and 35%, respectively. Overall yields for both anion exchange steps were 43% for the combination of flow-through and step elution mode. Combination of flow-through and linear gradient elution mode resulted in a yield of 44% for SIgA and 39% for SIgM. The proposed process allows the purification of biologically active SIg from animal whey in preparative scale. For future applications, the process can easily be adopted for purification of recombinant secretory immunoglobulin species.

Effects of lysosomal biotherapeutic recombinant protein expression on cell stress and protease and general host cell protein release in Chinese hamster ovary cells.

Recombinant human Acid Alpha Glucosidase (GAA) is the therapeutic enzyme used for the treatment of Pompe disease, a rare genetic disorder characterized by GAA deficiency in the cell lysosomes (Raben et al., Curr Mol Med. 2002; 2:145–166). The manufacturing process for GAA can be challenging, in part due to protease degradation. The overall goal of this study was to understand the effects of GAA overexpression on cell lysosomal phenotype and host cell protein (HCP) release, and any resultant consequences for protease levels and ease of manufacture. To do this we first generated a human recombinant GAA producing stable CHO cell line and designed the capture chromatographic step anion exchange (IEX). We then collected images of cell lysosomes via transmission electron microscopy (TEM) and compared the resulting data with that from a null CHO cell line. TEM imaging revealed 72% of all lysosomes in the GAA cell line were engorged indicating extensive cell stress; by comparison only 8% of lysosomes in the null CHO had a similar phenotype. Furthermore, comparison of the HCP profile among cell lines (GAA, mAb, and Null) capture eluates, showed that while most HCPs released were common across them, some were unique to the GAA producer, implying that cell stress caused by overexpression of GAA has a molecule specific effect on HCP release. Protease analysis via zymograms showed an overall reduction in proteolytic activity after the capture step but also revealed the presence of co‐eluting proteases at approximately 80 KDa, which MS analysis putatively identified as dipeptidyl peptidase 3 and prolyl endopeptidase. © 2017 American Institute of Chemical Engineers Biotechnol. Prog., 33:666–676, 2017

Synthesis of Aryl(2,4,6-trimethoxyphenyl)iodonium Trifluoroacetate Salts

The direct synthesis of aryl(2,4,6-trimethoxyphenyl)iodonium trifluoroacetate salts from aryl iodides is described. Stoichiometric quantities of trifluoroacetic acid and trimethoxybenzene are used as the counteranion and auxiliary precursors, respectively, under oxidizing conditions. The reaction occurs at mild temperature, is broad in scope, and does not require a separate anion exchange step to install the trifluoroacetate group. The intermediacy of two distinct dicarboxy aryl-λ3-iodanes is hypothesized in the mechanism.

The catalytic effect of anion-exchanged supported ionic liquid on aza-Michael-type addition

An effective synthesis of anion-exchanged supported ionic liquids using diatomaceous earth as solid support and its catalytic effect on the aza-Michael-type addition is described. Anionic polytungstophosphate and bisulfate ion are used in the anion-exchange step in catalyst design. In addition, the aza-Michael-type addition of various amines to 2- and 4-vinyl pyridine was examined in this article. The catalytic system can be separated from the reaction mixture and recycled in subsequent reactions. The structure of anion-exchanged supported ionic liquid on diatomaceous earth was studied by XRD, FT-IR, SEM, TGA and BET techniques. The structure of organic products was determined by 1HNMR, 13CNMR, FTIR, CHN and MASS spectroscopy.

Convenient N-Alkylation of amines using an effective magnetically separable supported ionic liquid containing an anionic polyoxometalate

An effective synthesis of anion-exchanged supported ionic liquid using magnetically separable nanoparticles and its catalytic effect on N-alkylation reactions is described. Anionic polyoxometalate derivative was used in the anion-exchange step in catalyst design. The catalytic system can be easily separated from the reaction mixture with external magnetic field and recycled in subsequent reactions. In order to evaluate catalyst repeatability, N-alkylation of some more amines such as Aniline, 4-aminobenzenesulfonamide, 4-methoxyaniline, 2-aminopyrimidin and 4,5,6,7-tetrahydrobenzo[d]thiazole-2,6-diamine in the presence of recoverable catalyst was successfully examined in this article. In addition, pramipexole dihydrochloride as an active pharmaceutical ingredient was successfully synthesized using the catalytic system. The structure of catalyst was determined by infrared spectroscopy, X-ray powder diffraction, and scanning electron microscope techniques. The structure of organic products was determined by 1H NMR, 13C NMR, infrared and Mass spectroscopy.